Effect of pneumococcal conjugate vaccination on serotype-specific carriage and invasive disease in England: a cross-sectional study

Background

We investigated the effect of the 7-valent pneumococcal conjugate vaccine(PCV7) programme in England on serotype-specific carriage and invasivedisease to help understand its role in serotype replacement and predict theimpact of higher valency vaccines.

Methods and Findings

Nasopharyngeal swabs were taken from children <5 y old and family members(n = 400) 2 y after introductionof PCV7 into routine immunization programs. Proportions carryingStreptococcus pneumoniae and serotype distributionamong carried isolates were compared with a similar population prior to PCV7introduction. Serotype-specific case∶carrier ratios (CCRs) wereestimated using national data on invasive disease. In vaccinated childrenand their contacts vaccine-type (VT) carriage decreased, but was offset byan increase in non-VT carriage, with no significant overall change incarriage prevalence, odds ratio 1.06 (95% confidence interval0.76–1.49). The lower CCRs of the replacing serotypes resulted in anet reduction in invasive disease in children. The additional serotypescovered by higher valency vaccines had low carriage but high diseaseprevalence. Serotype 11C emerged as predominant in carriage but caused noinvasive disease whereas 8, 12F, and 22F emerged in disease but had very lowcarriage prevalence.

Conclusion

Because the additional serotypes included in PCV10/13 have high CCRs but lowcarriage prevalence, vaccinating against them is likely to significantlyreduce invasive disease with less risk of serotype replacement. However, afew serotypes with high CCRs could mitigate the benefits of higher valencyvaccines. Assessment of the effect of PCV on carriage as well as invasivedisease should be part of enhanced surveillance activities for PCVs.Please see later in the article for the Editors'' Summary